This invention relates to a method of bonding an article to a wet perhalogenated polymer cation exchange membrane used in an electrochemical cell or, vice-versa, bonding such a membrane to an article.
The use of ion-permeable membranes in electrochemical cells, especially in chlor-alkali cells, is well known. In the present industrial practice, brine is electrolyzed to sodium hydroxide and chlorine in cells in which the electrodes are separated by a membrane which allows the cations and the anions to migrate to their respective electrodes while preventing undesirable ion migration and molecular migration. The most recently introduced membranes for chlor-alkali cells are made of a fluorocarbon resin and contain pendant sulfonic acid (--SO.sub.3 H) and carboxyl (--COOH) groups. Those different groups may be located on the same polymer, on different polymers in a blend, or on different polymers forming separate layers, one with pendant --SO.sub.3 H groups and the other one with pendant --COOH groups, normally in ionic form, such as, e.g., sodium or potassium salts.
The membranes are clamped within the electrochemical cells in an arrangement which divides each cell into tightly separated compartments, so that there is no physical transport or leakage of the electrolyte from one compartment to the other. Because such tight clamping requires good dimensional stability of the membrane under the operating conditions to avoid wrinkling and folding, the membranes normally are presoaked either in water or in a solution such as aqueous sodium hydroxide or sodium bicarbonate, whereupon they swell and expand to a size which is substantially maintained during the the electrolysis.
However, in their wet swollen condition those membranes do not have as high mechanical strength as in the dry state, and especially do not have good tear strength, so that any cuts or notches on their periphery propagate readily under the usual handling or clamping conditions, thus causing membrane failure with a possible safety hazard and resulting disruption of the operation and economic loss. One important application of this invention is in reinforcing the periphery of the membrane sheet to prevent membrane tearing, especially as a result of notch or cut propagation. Other applications include, e.g., bonding a gasket to the periphery of the membrane or bonding the membrane itself to a supporting frame of metal, plastic, or another material.